In connection with his study of the stars, Herschel undertook to measure their distances from the earth, and to find out if their brightness depended upon their nearness to or remoteness from us. And after a long series of careful experiments, he determined that if stars of the first magnitude, like Sirius and Arcturus, were removed twelve times their actual distance, they would be just visible to the naked eye, while if stars which are only now to be seen through a telescope were to be brought nearer to the earth so as to be only one-tenth as far away as they now are, they would shine with the brightness of the largest and most brilliant stars. He concluded, therefore, that the brightness of the stars depended on their distance, and that the fainter stars were the more distant ones, and even devised a method based on this idea by which their relative distances would be ascertained.

It is now known that he was wrong in this view, for some of the faintest stars have been found to be among those nearest the earth; but the difficulties met in determining star-distances are so great that it was not till sixteen years after the death of Herschel, and when the instruments for making observations had been greatly improved, that the distance of a fixed star was actually measured. Herschel's investigations and experiments on the light of the stars and their distance led the way to some of the most valuable and wonderful results of modern astronomical research and have given him the position of a pioneer in the science.

In connection with these studies, Herschel also took up the subject of the nature of the sun and its place in the universe. The accepted theory of the sun's nature was that it was a solid, surrounded by a luminous atmosphere which gave it its brightness, and this theory, with some changes, was also held by Herschel. But his deductions in regard to the sun's place in the universe were of more importance. His discovery of the revolution of double stars could only lead to speculation with regard to all the objects of creation, and it was but natural to conclude that motion, which was a property of so many, should belong to all.

Observations extended from the time of the ancients had led to the conclusion that some of the largest stars of the first magnitude had changed their places within the historic period, and they were therefore supposed to have an individual motion, and from this fact Herschel argued a corresponding motion for the sun, which he decided was itself a small star. He therefore began a series of experiments, and finally came to the conclusion that the sun, with all his attendant company of planets and comets, was in reality moving through space at a marvellous rate of progress, and that, in accordance with the law of gravitation, he was passing through an orbit of inconceivable magnitude having for its centre one of the remote stars.

It has been thought that this great central fire whose mighty forces thus govern the of the solar system is the star Alcyone, in the Pleiades, but of this we cannot be sure. We only know that the sun, with his great retinue of revolving worlds, is moving toward some unknown point in the heavens, and that the stars, which were once thought to be brilliant globes firmly fixed in crystal spheres, are in reality probably the centres of attendant planets which they carry with them in their majestic progress through the boundless regions of space; and that, if it were possible to view the heavens as they really are, we should see an infinite number of such systems, with orbitals crossing and recrossing, in the most intricate manner, but in place of the apparent confusion and entanglement there exist the most exquisite order and symmetry.

Herschel's study of the heavens also included observations on those cloud-like appearances called nebulæ which are seen in various constellations, and of which the Milky Way is the greatest example.

From the earliest times this broad band of light had attracted the attention of mankind, and many quaint legends were connected with it. The Romans called it the Highway of the Gods, and in later times it was sometimes spoken of as Jacob's Ladder;  but even among the ancients some true idea of its character existed, for Pythagoras declared that the Milky Way was only a great assemblage of stars, and Galileo's telescope had proved that in the main the theory of the old Greek was correct. At first Herschel was led to believe that all nebulæ could be seen to be made up of stars, if viewed through a sufficiently powerful telescope. But later he changed his opinion, and came to the conclusion that there were two kinds of nebulæ—the resolvable, which are made up of great star-clusters which have a cloudy appearance from their immense numbers and great distance, and the irresolvable, which are immense masses of self-luminous matter which gradually is condensing into solids like the sun and stars. This last idea was not new to Herschel, for Tycho Brahé and Kepler had both suggested that the "new stars" which appeared from time to time might be caused by the condensation of the ether which filled all space. And although all "new stars" are really believed now to belong to the temporary stars which appear and disappear with regularity, yet the thought that the universe had been evolved out of such matter shows in a marked degree the originality and boldness of Kepler's genius.

The French astronomer Laplace, a contemporary of Herschel, also held this theory of the nebulæ, which he published in a work called the "Nebular Hypothesis."

Laplace conceived that the solar system consisted originally of matter in the form of gas or vapor of an enormously high temperature; that as it cooled unequal currents were formed, which gradually caused it to rotate; that its rate of motion increased until the outside, which was of a lower temperature than the centre, would become detached and break up into smaller parts; that these parts came together finally and formed spheroidal masses which revolved around the centre; that the sun was what was left of the original matter, and the planets and asteroids were the parts that had been thrown off. This theory, which had its foundation in the action of the law of gravitation, may apply not only to the solar system but to the entire universe, and Herschel's idea of the irresolvable nebulæ, consisting of a shining fluid which was solidifying into stars, has been supported by later astronomers, for when the light from these nebulæ has been analyzed it has given out the colors of matter in a state of gas, while an analysis of the light of the stars gives a very different result.

And thus Herschel's comparison of the heavens to a flower-garden may be seen to have a deeper significance than would at first appear; and if we consider the claims of the nebular hypothesis, we might say that the nebulæ are the great seed-repositories of nature, from which are evolved all the stars and planets which, passing through the time of bloom and maturity, come at last to a state resembling that of the dead moons—the withered flowers of these celestial gardens—from which all life has passed away.

Herschel made many observations on light and heat in connection with his other studies, but he is chiefly remarkable for his exhaustive survey of the stars.

He died in 1822, at the age of eighty-four, preserving his great mental powers till the last, and claiming, with truth, that he had looked farther into space than any other eye had yet penetrated.

The nebular hypothesis which his researches helped to formulate is as yet but an unproved theory, and whether it embodies the true secret of creation or not we cannot tell.